The bones of the arm make up the structure of the upper limb, which helps you do many everyday movements like lifting, pushing, pulling, and rotating. 

These movements are important for simple tasks such as writing, carrying bags, opening doors, throwing a ball, and reaching for things. The arm bones are strong but also flexible, which makes it possible to move your arm in many directions while still being able to support weight and keep the arm steady.

Humerus

The humerus is a long bone in the upper arm. It stretches from the shoulder to the elbow.

The top (proximal) end of the humerus connects to the shoulder blade (scapula) at a joint called the shoulder joint (glenohumeral joint). The bottom (distal) end of the humerus connects to two bones in the forearm: the radius and the ulna, at the elbow joint.

Unlike many other bones, the humerus has two necks:

• The anatomical neck is near the head of the bone and marks where the growth plate used to be (the area where the bone grew during childhood).

• The surgical neck is lower down and is the most common place where the humerus breaks.

Ulna & Radius

The ulna is one of the two long bones in the forearm. It is on the inner side (closer to the body) and stays mostly still, helping to keep the forearm stable. The radius, the other forearm bone, is on the outer side (further from the body) and can rotate around the ulna to help the forearm and hand move.

When comparing the two forearm bones in the same person, the radius is usually shorter and thicker than the ulna.

The ulna connects to:

• The humerus at the elbow joint (top end)

• The radius at the distal radioulnar joint (near the wrist)

The radius connects in four places:

1. Elbow joint – where the head of the radius meets the humerus.

2. Proximal radioulnar joint – where the top of the radius meets the ulna.

3. Wrist joint – where the end of the radius meets the wrist bones.

4. Distal radioulnar joint – where the end of the radius meets the ulna again near the wrist.

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